Satellite images capture monumental ruins surrounded by bizarre feather-shaped structures on a Welsh mountaintop; experts investigate a hidden tunnel containing the remains of an abandoned slate mine with an exploitative and deadly past.

Satellite images capture the Hill of Tara, two conjoined circular structures embedded in Ireland's lush and rolling landscape. Experts investigate the ancient site used to crown the legendary High Kings of Ireland at the Stone of Destiny and the elusive hunt for the Ark of the Covenant by the British Israelites in the 1890s.